Cochlear Implants in Developing Countries - Vula - University of ...

acoustic input into a usable electricaldynamic range for each electrode which isstimulated.The audiologist who does the programming/MAPpingis responsible for maintenanceand programming of the CI, includinginitial stimulation and regular followupprogramming sessions. The audiologistobtains 2 psychophysical measures i.e.elec-trical thresholds (T-levels) andcomfort levels (C-levels), to create aprogram (MAP).An appropriate encoding strategy as wellas a stimulation mode should be selectedfor each patient. Encoding strategy is themeans by which an implant translates theincoming acoustic signal into patterns ofelectrical pulses which in turn stimulate theauditory nerve fibres. Stimulation moderefers to the flow of electric current, that is,the location of the indifferent (reference)electrode relative to the active (stimulated)electrode. A combination of objective andbehavioural programming techniques areutilised to establish an appropriate MAPfor each CI recipient.Bilateral CIsIn the developed world, children andgrowing number of post-lingual deaf adultpatients are commonly implanted. Implantingbilateral CIs means that 2 separateinternal and external hardware systems areimplanted either concurrently or sequentially.The speech processors do not communicatewith one another and programmingMAPs are done independently foreach processor.Advantages of bilateral CIs include:Improved sound localisationImproved speech understanding inquiet conditions as well as with backgroundnoiseBoth auditory pathways are stimulatedwhich ensures that the better performingear has been implanted (since it isdifficult to determine pre-operativelywhich ear will perform better with aCI)The 2 nd CI acts as a reserve should oneof the implants failEnsures binaural hearing and thusassists in a young child’s developmentof central auditory processing skillsThe ideal bilateral adult CI candidate haspost-lingual hearing loss and a relativelyshort duration of profound hearing loss(